The world is my country, all mankind are my brethren, and to do good is my religion.

Thomas Paine (1737-1809) American political philosopher and writer

(Attributed)

This is widely attributed to Paine, in respectable sources, and usually (when a source is given) from The Rights of Man (1791) or The Age of Reason (1795). But a search of the text of the latter shows none of the three clauses appear in it. In The Rights of Man, Paine did write, "My country is the world, and my religion is to do good," which is close but not the same (and is sometimes cited with the different word order of the subject quote).

The three clauses appear (with a fourth, "I believe in One God and no more") on the 1923 plaque at the location of Paine's last residence, on Grove St. in Greenwich Village, NY, but with no citation (though one is sometimes applied). But the attribution of this phrase to Paine (including citing it to The Age of Reason) predates the plaque (e.g., 1913). I've not been able to find a reliable citation for this quote.